Correlation between the γ passing rates of IMRT plans and the volumes of air cavities and bony structures in head and neck cancer

Abstract

Background Both patient-specific dose recalculation and γ passing rate analysis are important for the quality assurance (QA) of intensity modulated radiotherapy (IMRT) plans. The aim of this study was to analyse the correlation between the γ passing rates and the volumes of air cavities (Vair) and bony structures (Vbone) in target volume of head and neck cancer. Methods Twenty nasopharyngeal carcinoma and twenty nasal natural killer T-cell lymphoma patients were enrolled in this study. Nine-field sliding window IMRT plans were produced and the dose distributions were calculated by anisotropic analytical algorithm (AAA), Acuros XB algorithm (AXB) and SciMoCa based on the Monte Carlo (MC) technique. The dose distributions and γ passing rates of the targets, organs at risk, air cavities and bony structures were compared among the different algorithms. Results The γ values obtained with AAA and AXB were 95.6 ± 1.9% and 96.2 ± 1.7%, respectively, with 3%/2 mm criteria (p > 0.05). There were significant differences (p < 0.05) in the γ values between AAA and AXB in the air cavities (86.6 ± 9.4% vs. 98.0 ± 1.7%) and bony structures (82.7 ± 13.5% vs. 99.0 ± 1.7%). Using AAA, the γ values were proportional to the natural logarithm of Vair (R2 = 0.674) and inversely proportional to the natural logarithm of Vbone (R2 = 0.816). When the Vair in the targets was smaller than approximately 80 cc or the Vbone in the targets was larger than approximately 6 cc, the γ values of AAA were below 95%. Using AXB, no significant relationship was found between the γ values and Vair or Vbone. Conclusion In clinical head and neck IMRT QA, greater attention should be paid to the effect of Vair and Vbone in the targets on the γ passing rates when using different dose calculation algorithms.

Dose difference between anisotropic analytical algorithm (AAA) and Acuros XB (AXB) caused by target’s air content for volumetric modulated arc therapy of head and neck cancer

“…It means that the dose difference between the D 95% prescription and others becomes more pronounced. Although the dose differences between AAA and AXB for IMRT and VMAT decrease because of dose compensation from out of field [ 9 , 17 ], the dose differences between calculation algorithms are large when the target’s air content is large.…”

Guía para el control de calidad y seguridad de los sistemas de planificación y planes de tratamiento de radioterapia externa

“…Consideran además como buena práctica establecer diferentes tolerancias en función de la complejidad de la técnica, algo que se refleja también con frecuencia en la bibliografía. [268][269][270][271] Una consecuencia de dicha retroalimentación podría ser modificar o adquirir nuevo equipamiento o mejorar el entrenamiento del personal.…”

Dosimetric performance evaluation of the Halcyon treatment platform for stereotactic radiotherapy: A pooled study

“…[61] Standard collection tools of gamma passing rates are 2D or 3D matrix devices and tools that come with the accelerator manufacturer, such as Varian portal dosimetry (PD). The patient anatomical site variations and structural differences, [62] TPS algorithms, [63] plan complexity, [47] and device accuracy [64] will likely affect gamma passing rates. Halcyon's gantry rotation speed and MLC motion speed are faster than C-arm accelerators, so the dose delivery accuracy of SRT plans is a problem worth studying.…”